An in-plane insensitive multiaperture speckle shear interferometer for slope measurement
TL;DR: A modified two-aperture speckle shear interferometer that eliminates the contribution of the in-plane component and its derivative to the phase change, and yields a fringe pattern corresponding to the first-order partial derivatives of the out-of-plane displacement component, is reported in this article.
Abstract: A modified two-aperture speckle shear interferometer that eliminates the contribution of the in-plane component and its derivative to the phase change, and yields a fringe pattern corresponding to the first-order partial derivatives of the out-of-plane displacement component, is reported in this note. In this method, two laterally sheared object points are viewed axially. The wave fields from these points are independently combined at the image plane of the imaging system.
Citations
More filters
TL;DR: In this article, optical configurations for DSPI and DS with a double aperture mask in front of the imaging lens for spatial phase shifting are proposed for the measurement of out-of-plane displacement and its first order derivative (slope) respectively.
Abstract: Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are well known optical tools for qualitative as well as quantitative measurements of displacement components and its derivatives of engineering structures subjected either static or dynamic load. Spatial phase shifting (SPS) technique is useful for extracting quantitative displacement data from the system with only two frames. Optical configurations for DSPI and DS with a double aperture mask in front of the imaging lens for spatial phase shifting are proposed in this paper for the measurement of out-of-plane displacement and its first order derivative (slope) respectively. An error compensating four-phase step algorithm is used for quantitative fringe analysis.
99 citations
TL;DR: In this article, a (1,N) spatial phase-shifting technique in DSPI and DS for non-destructive evaluation of quasidynamic behavior of objects subject to slowly varying loads is described.
Abstract: Digital speckle pattern interferometry (DSPI) and digital shearography (DS) are two independent useful whole-field noncontacting optical methods for nondestructive flaw detection and precision measurements. We describe a (1,N) spatial phase-shifting technique in DSPI and DS for nondestructive evaluation (NDE) of quasidynamic behavior of objects subject to slowly varying loads. The technique employs a double-aperture arrangement in front of the imaging system to introduce spatial carrier fringes within the speckle. The prominent advantage of the proposed technique is it requires only a single frame prior to the object deformation and a number N of frames during the object deformation for NDE. Quantitative measurement of a defect and its behavior in loading conditions are studied by recording spatially phase shifted frames before and during thermal stressing of the object for continuous deformation variation with time. Experimental results on a polymethyl methacrylate (PMMA) panel using an error-compensating five-phase-step algorithm for quantitative NDE using both DSPI and DS are demonstrated.
8 citations
01 Jan 2022
6 citations
References
More filters
TL;DR: In this article, a three-aperture speckle shear interferometric technique is introduced to separate the in-plane displacement and slope contributions from the shear Interferogram.
Abstract: An imaging system with its aperture fully open or with a multiaperture mask in front has been used for carrying out speckle shear interferometry. The shearing is achieved by installing shear elements in front of the imaging system. The multiaperture configuration has built-in in-plane displacement sensitivity, and hence shear fringes obtained from multiaperture shear interferometer always carry the in-plane displacement contribution. This problem does not arise when the full aperture of the lens is used. A three-aperture speckle shear interferometric technique is introduced here to separate the in-plane displacement and slope contributions from the shear interferogram. Detailed theoretical and experimental results are presented.
32 citations
TL;DR: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil to obtain the moire curvature pattern.
Abstract: Speckle and speckle-shearing interferometer geometries have been combined into a single setup by the use of a small ground glass reference diffuser on the lens pupil. Sheared fields are obtained with a split lens arrangement. Judicious aperturing results in separated diffraction halos at the FT plane. Fringe patterns corresponding to out-of-plane displacement and slope are obtained by filtering via the appropriate halos. A four-aperture arrangement coupled with shearing elements extends the method to obtain the moire curvature pattern.
27 citations
TL;DR: In this paper, a theoretical analysis of two allied laser speckle interferometric techniques for measuring surface displacement and strain was carried out for the cases when a generalized deformation of the surface under study takes place.
Abstract: This article deals with a theoretical analysis of two allied laser speckle interferometric techniques for measuring surface displacement and strain. One technique uses a Double Aperture Speckle Camera, and the other uses a similar interferometer called a Double Aperture Speckle Shearing Camera. These techniques, although developed elsewhere, had not been analysed for the cases when a generalized deformation of the surface under study takes place. Such an analysis was done and is presented here in an abbreviated form. It results in ‘new’ equations governing the formation of fringes by the two cameras. Various solution methods of these equations are outlined and discussed.
21 citations
TL;DR: It is shown theoretically and experimentally that the use of a single aperture is essential for obtaining the proper value of the deflection slope of an object: the single-aperture method enables us to obtain the proper slope distribution regardless of the direction of displacement.
Abstract: The difference in the information obtained by the single-aperture and the double-aperture methods in speckle shearing interferometry is discussed. It is shown theoretically and experimentally that the use of a single aperture is essential for obtaining the proper value of the deflection slope of an object: the single-aperture method enables us to obtain the proper slope distribution regardless of the direction of displacement. With the double-aperture method, however, proper distribution can be obtained only for displacement in a particular direction, and this introduces an error into the slope measurement.
18 citations